1. Technical Field
The present disclosure generally relates to electronic circuits and, more specifically, to so-called class-AB amplifiers.
The present disclosure more specifically applies to audio or audio/video signal processing chains.
2. Description of the Related Art
In most audio or audio/video devices, signals received by an antenna, extracted from a tape, from a CD/DVD, from a mobile telephony network, etc. are, possibly after reprocessing, amplified to be exploited by a playback device (television set, home cinema, cell phone, etc.) equipped with a decoder. Most often, such signals transit from one device to another or within a device, in compliance with the levels provided by standards. For example, for audio signals, a DOLBY standard sets the maximum excursion of audio signals to 2 volts RMS (approximately 5.6 volts peak to peak).
FIG. 1 is a simplified representation of a processing chain of the type to which the present disclosure applies as an example. In this example, audio signals originating from an antenna 11, from a video tape 12, or from a digital system 13, are processed by one or several circuits 2 (AUDIO PROC.) before being amplified (block 3, AMP.) to be provided, for example, to a scart connector 4. The processing (demodulation, filtering, path separation, etc.) performed by circuits 2 is different according to the audio source, but the signal(s) provided by the circuit must all be amplified, for example, to respect the DOLBY standard at the output. Other audio or video signals reach scart connector 4 (arrow in dotted lines 15). Such signals originate from parallel processing paths. In particular, for stereo signals, left-hand and right-hand paths are amplified separately (while possibly sharing a same upstream circuit 2).
Processing and amplification functions 2 and 3 are generally carried out by circuits powered under different voltages V1 and V2 (V2 being greater than V1) and made in different technologies, that is, with transistors capable of withstanding different voltages. Taking the example of the DOLBY standard, voltage V2 is on the order of 8 volts while the processing circuits are powered under a lower voltage V1, for example, on the order of 3.3 volts. For simplification, reference will be made hereafter to high and low voltages, but these voltages keep the same order of magnitude (there is no switching from a low voltage of a few volts to a high voltage of some hundred volts).
Further, although reference will be made in the following description to the provision of audio or video signals by a scart connector, the present disclosure more generally relates to any transmission of audio signals from one circuit to another or from one circuit portion to another in which similar problems are posed.
It would be desirable to be able to integrate the entire processing chain in a same integrated circuit. However, making this circuit in the technology adapted to the highest voltage adversely affects the bulk and generates an unnecessary consumption in the processing portion.
It would thus be desirable to make the amplifier in the low-voltage technology. Another problem then arises, which is that the transistors of this low-voltage technology do not stand the high voltage used to provide the amplified signal with the desired output deviation.